EFFECT OF ORIGINAL MANUFACTURING DEFECTS/OPERATIONAL WEAR ON OLDER PACKAGES SAFETY REPORTS

MOPDT (Magnox Operating Programme Delivery Team) are responsible for the safe delivery of irradiated fuel from the remaining fuelled Magnox Ltd sites in the UK and Dounreay (Scotland) site to the Sellafield reprocessing facility. The fuel is transported in a fleet of 42 Type B(M) cuboidal transport flasks (referred to herein as M2 flasks), the transport of which is regulated by the ONRRMT (Office of Nuclear Regulation, Radioactive Material Transport). Approximately 7-8 flask transports are completed in a typical week. The current Magnox Operating Programme, which defines Magnox sites generation and defueling periods, predicts that fuel shipments will continue until around 2019. This paper looks at the effect original manufacturing defects/operational wear in older packages can have on the Package Design Safety Report when identified using more modern inspection techniques than those used during original manufacture. In particular, a recent case study to justify sub surface indications in the cooling fin to main body full penetration welds will be referenced. This work package involved ultrasonic inspections (not utilised during original manufacture), structural integrity and thermal finite element analysis exploring the effect sub surface indications in the cooling fin welds have on the M2 flasks performance during normal transport and the regulatory accident conditions. Based on the conservative assumption of complete loss of a number of cooling fins, the defects have been justified through analytical calculations of normal transport conditions and producing evidence of flask performance during the regulatory accident. This work has increased knowledge in the effects of definning and the levels of redundancy within the M2 flask design. The final area of this paper looks at how Magnox Ltd is currently taking a pro-active approach to highlighting potential engineering challenges within an ageing flask fleet. This has included a thorough independent review of the flask design and history, concluding in further on-going work packages, for example reviewing original manufacturing/inspection records, determining rate of thread wear and strategic procurement of spares. Conclusions will be drawn to support recommendations for modern RAM transport package design, assessment, operation and maintenance to mitigate as far as practicable the risk of original manufacturing defects/operational wear, identified through modern inspection techniques, challenging the on-going use of the package